Supercars gain from new type of electric motor

Jon Lawson

The performance of EVs and hybrids is being unlocked by new electric motors technology, says the MD of the firm that’s developed a new solution in this area.

The automotive industry is undergoing the most rapid and radical transformation since its inception over a century ago. At the centre of this is the electric powertrain – and the electric motor. Ian Foley is managing director of Equipmake, a company that can call on F1 experience, and has developed a new type of electric motor, for hypercars and buses alike.

“There’s no doubt that the industry wants smaller, lighter, more powerful and more efficient motors,” explains Foley. “And it wants them at a reasonable price. And it wants them yesterday. No pressure, right?”  Foley continues, “At Equipmake, we’ve created what we believe is the world’s most power/torque dense electric motor. And although its performance is industry-leading, this is a motor that can be mass produced at a price that’s right.

“So how come we think we’re ahead of the competition? Well, although electric powertrain technology may have come a long way in the past 10 years, when it comes to electric motors, there is one exciting concept where development has been held back for a variety of reasons: the ‘spoke’ motor.”

Foley explains that, “A spoke motor is a type of permanent magnet motor where the magnets are arranged like the spokes of a wheel, making the best use of the magnetic flux. This type of architecture isn’t new. A number of large companies (such as General Electric) have written papers on the benefits of the spoke design, but it has not been widely adopted because no-one has figured out how to build one cost-effectively.

“Right now, the vast majority of magnet motors in automotive applications use magnets arranged in V-shaped laminations around the hub. This was the design originally used in the Toyota Prius and has since been adopted by most of the industry, because there’s a well-known route to low cost manufacture.”

He adds, “However, it’s certainly not the most efficient or most powerful or most compact. The key to everything with an electric motor is cooling.”

A cool idea for electric supercars

Foley states that, “The powerful rare earth magnets used in high-performance electric motors require significant cooling to ensure optimum performance. Under constant high-load operation, they must be kept within a specific temperature window. This is why electric motors are often quoted with two power figures: peak power and continuous power. The first is a measure of flat-out performance and the latter is the level of continuous power output the motor is capable of sustaining without overheating and shutting down.

“In the common V-shaped design, it is difficult to circulate coolant close enough to the surface of the magnets. The only alternative is to use expensive magnets whose performance does not degrade at higher temperatures, which has obvious cost implications.”

Foley details how, by arranging the magnets at 90° to the hub, ‘spokes’ are formed, between which the laminations run. He says that this orientation provides a much-improved use of the magnetic material: providing 25% more torque for a given electrical output or, equivalently, the same torque for 25% less electrical energy. “Essentially, it means that our motors have class-leading torque and power density.”

Foley adds: “The spoke arrangement then crucially allows us to pump water inside the hub and cool the surface of the magnet more directly. This enables us to use cheaper rare earth Neodymium magnets while maintaining high performance, thus addressing one of the primary criticisms of magnetic electric motors: raw material cost.”

Rare earth prices can be volatile and the cost of the magnets certainly does make up a considerable portion of the motor’s total raw material cost – around 50%. By the time the motor is manufactured however, the magnets account for only 15% of the processed bill of materials.

Why? “Well, it’s important to look at the cost of the motor’s rare earth materials relative to the entire electric powertrain,” explains Foley. “Much of the total raw material cost is dependent on the size of the battery. In using lighter, more efficient and more powerful electric motors, less battery capacity is required for the vehicle to achieve a specific range.

“This results in a smaller battery that requires less raw material while also improving vehicle packaging. Volatility in the Neodymium cost is therefore easily manageable.

“We’ve also worked out how to scale up the whole motor for mass production. We use a cheap aluminium hub, which is forged, so a very low cost method of manufacture, while the way we interlock the laminations – what holds the magnets in place – is a design, including the cooling system, which we’ve patented.”

Foley reveals that all of the processes and materials used are standard processes. “So, the fact that the motor smaller and lighter means that it’ll be cheaper. There’s nothing in the design or manufacture that involves an expensive process that isn’t being used for motor manufacture at the moment,” he comments.

Motorsport inspired electric motors

Some of the background knowledge in developing the new spoke motor has come from motorsport. Foley details: “In the early 2000s, Equipmake was doing research into electric motors and flywheels as we knew that F1 powertrains were going to go hybrid. We proposed the idea of a flywheel to the FIA, which they liked. The result was that we began working with Williams and the system went on to be used to great success in 2009. The high-speed flywheel developed for this programme was effectively a composite electric motor and Equipmake has built on that learning since then.”

Fast-forward to the present and the firm’s spoke motor is capable of high power and torque output, in a compact package that is smaller and cheaper to manufacture than more conventional configurations. Foley states: “Our APM200 motor, for example, weighs just 40kg and produces 220kW and 450Nm at up to 10,000rpm. Compared to a conventional motor of very similar performance (in terms of peak and continuous power), we’re about 50% of the volume and 80% of the mass.

To further put that into context, on a kW/kg basis any electrical engineer would be overjoyed with an output of 4 kW/kg. Our APM 200 motor puts out 5.5kW/kg and the technology can be tuned to make as much as 15 kW/kg.”

Since the company’s early days designing F1 hybrid flywheels, its development of future powertrain solutions has progressed greatly. Taking a novel approach to electric motor design and production has meant that its designs are already being adopted by manufacturers.

The new Ariel Hipercar – a 1180bhp range-extended electric supercar – will use four of Equipmake’s APM200 motors. As a testament to the technology’s versatility, it has has also adapted the same motor for use in commercial vehicles.

Foley adds, “Two APM200 motors will power a new electric bus we are developing with Brazilian company Agrale, the production version of which will arrive on the streets of Buenos Aires, Argentina, in 2020.”

He concludes that, “Although change can be turbulent and testing, the automotive industry’s drive toward electrification is also a wonderful opportunity for innovation. Manufacturers of EVs are striving to strike the crucial balance between battery cost, motor cost and performance. The spoke motor is already making waves in specialised applications, the next challenge for us is to truly tackle the mass market. And not just in automotive, but in aviation and marine too.”

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